On an August afternoon in Washington, D.C., typically miserable for its heat, humidity and stillness, reporters gathered at a downtown hotel not known for its air-conditioning. Stuffed inside a windowless conference room that was being heated still further by the television people’s lights, we waited for Michael J. Wallace, who had been trying, in fits and starts, to unveil nuclear power’s second act.

On arrival, Wallace, a meticulous manager not known for ad-libbing, looked out over the sweating reporters and smiled. “It’s days like today that highlight the real need for new, emissions-free, baseload power,” he said. Unless we get started soon, he added, rolling blackouts could become the norm.

Wearing a suit and tie and seeming to enjoy the heat, Wallace announced that his company, UniStar Nuclear Energy, a partnership between Constellation Energy and the European nuclear consortium Areva, was looking to build a new kind of nuclear power plant in the U.S. and elsewhere. “I’m pleased to say I played a role in the last round of nuclear power plant development, and I’m really pleased to be involved,” the chairman said, calling to mind a graying astronaut who walked on the moon years ago and now wanted to do it again.

That was in 2006. Since then, Wallace has intermittently made new announcements about incremental progress toward building a new reactor about 45 miles south of Washington, which could be the first U.S. nuclear plant put on order and built since 1973. Wallace’s original feat was leading the start-up of two of the nation’s last big nuclear plants, completed in 1987 in Illinois. Like another moon shot, the launch of new reactors after a 35-year hiatus in orders is certainly possible, though not a sure bet. It would be easier this time, the experts say, because of technological progress over the intervening decades. But as with a project as large as a moon landing, there is another question: Would it be worthwhile?

A variety of companies, including Wallace’s, say the answer may be yes. Manufacturers have submitted new designs to the Nuclear Regulatory Commission’s safety engineers, and that agency has already approved some as ready for construction, if they are built on a previously approved site. Utilities, reactor manufacturers and architecture/engineering firms have formed partnerships to build plants, pending final approvals. Swarms of students are enrolling in college-level nuclear engineering programs. And rosy ­projections from industry and government predict a surge in construction.

Modern competitive pressures complicate the matter, however. For one thing, in much of the country any new construction would be by “merchant generators”—independent companies rather than large, monolithic utilities. Nuclear power was simpler two decades ago, because utilities built their own plants and could usually pass costs through to captive consumers no matter how big the overruns. But in states such as Texas, Maryland and New York, where the public service commission has separated the generation of electricity from power transmission and distribution, there is no longer a cushion for a generation company that guesses wrong. Such plants must sell electricity at whatever price the market will bear.

That number is hard to predict, because although reactors would exploit current technologies and techniques, so will modern coal and natural gas plants. Gas, especially, has much lower up-front costs, a big consideration if credit remains tight. And gas plants can be built in small units in only three or four years, as compared with six or eight for mammoth reactors.

For nuclear power, the modernization is intended to produce dramatic differences: plants that will run more than 90 percent of the hours in a year and last for 60 years or longer. The ones in service today ran only about 60 percent of the time when they were new and were assumed to have only a 40-year life. But utilities are already signing long-term contracts for large solar generators, and wind turbines are being erected at an unprecedented rate. Those alternatives operate fewer hours of the year, but with no burden of fuel cost or fuel-disposal problems the price of power they produce could be low enough to squeeze nuclear power out of the mix.